The invention discloses a method and a device for detecting laser wavelength based on Rayleigh Brillouin scattering. The Rayleigh Brillouin scattering spectrum in a certain scattering direction is obtained by measuring a Rayleigh Brillouin scattering signal produced by the interaction between laser of which the wavelength is to be detected and high-pressure gas, and the wavelength of the laser tobe detected is obtained according to the frequency shift of the Brillouin peak. Wavelength detection of laser from ultraviolet to infrared can be realized by using one set of device. Moreover, the device can control the temperature and pressure of gas in a scattering pool according to whether the wavelength to be detected is in the ultraviolet, visible light or infrared band to optimize the measurement of spectral Brillouin frequency shift and signal intensity. The signal intensity and spectral resolution can be improved, and it can be ensured that the detection result is highly accurate. . The invention mainly describes a device for realizing laser wavelength detection by using spontaneous Rayleigh Brillouin scattering.